1,3-Dihalo-5,5-dialkylhydantoins are effective as biocides for aqueous systems such as industrial cooling water, recreational water, and wastewater.
Widely used for such purposes are N,Nxe2x80x2-bromochloro-5,5-dialkylhydantoins. One of the features emphasized for such materials is that in use, the chlorine released from the biocide regenerates active bromine from inactive bromide species formed during the water treatment operation. In other words, the chlorine atom in the initial N,Nxe2x80x2-bromochloro-5,5-dialkylhydantoin is in effect regarded as a precursor for additional active bromine for sanitation purposes.
As is well known in the art, a deficiency of chlorine, of hypochlorites, and of certain halogenated organic water-treating agents is the formation, during usage, of undesirable disinfection by-products. These by-products are undesirable both from the standpoint of environmental concerns and also from the standpoint of toxicological considerations.
Another very serious problem in connection with water disinfection is biofilm development. Biofilms are bacterial films which tenaciously adhere to surfaces in contact with water such as heat exchanger surfaces, conduit interiors, filters, and other processing equipment. These films are very undesirable because they can harbor dangerous pathogens, and cause damage to the surfaces to which they have become attached. Moreover, the bacteria form a slime layer of extra-cellular polysaccharide which affords protection to the bacteria and in addition constitute an effective barrier against penetration of biocidal agents used in an attempt to combat such bacteria. In situations where the water is prone to development of calcium carbonate scale, the presence of such gelatinous extra-cellular polysaccharides can result in the formation of layers of scale bonded to the substrate surface by the gelatinous polysaccharides. Polysaccharide films and films of scale bonded by means of polysaccharides can greatly interfere with the operation of heat exchangers by virtue of their insulating characteristics, and can markedly interfere with the functioning of filters and the flow of water through pipes and conduits by virtue of the clogging tendencies of such polysaccharide films.
Thus a need exists for a biocidal agent which is highly effective in providing biocidal control, especially eradication, or at least minimization, of biofilms in water systems, and in addition, a biocidal agent which has the capability of providing such biocidal control even though used at very low concentrations in water.
This invention involves, inter alia, the surprising discovery that 1,3-dibromo-5,5-dimethylhydantoin when used in treating water achieves the requirements mandated by the U.S. Environmental Protection Agency at a dosage level that is only one-half of that required when using one or a mixture of N,Nxe2x80x2-bromochloro-5,5-dialkylhydantoins. This discovery enables the use of extremely small concentrations of the. 1,3-dibromo-5,5-dimethylhydantoin to effectively sanitize water while at the same time achieving excellent microbiological control. Further, the ability to effectively utilize such small concentrations is expected to result in significant reduction in formation of disinfection by-products.
Another important facet of this invention is the fact that so far as is presently known, 1,3-dibromo-5,5-dimethylhydantoin has never before been used as the sole disinfecting agent for sanitizing water. Instead, in the prior art, only when in admixture with much larger quantities of N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin was 1,3-dibromo-5,5-dimethylhydantoin deemed suitable for use in water sanitation.
Another totally unexpected benefit resulting from the use of 1,3-dibromo-5,5-dimethylhydantoin in water systems is its exceptional effectiveness in destruction and removal of biofilm. Indeed, 1,3-dibromo-5,5-dimethylhydantoin has been found to be almost twice as effective in biofilm eradication as N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin and even more effective in this regard than a number of other known biocidal agents. Because of such great effectiveness, 1,3-dibromo-5,5-dimethylhydantoin can be effectively utilized for biofilm control at extremely low concentrations. This in turn results in substantial benefits from an environmental standpoint and from the standpoint of operating costs.
More particularly, it has been discovered that in the AOAC Official Method: Disinfectants For Swimming Pools (also referred to as Presumptive Efficacy Test) only 1 milligram of bromine (as Br2) from 1,3-dibromo-5,5-dimethylhydantoin per liter of water satisfies these official requirements for labeling purposes. In sharp: contrast, parallel tests conducted using N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin required 2 milligrams of bromine (as Br2) per liter of water in order to satisfy these official requirements.
Similarly, it has been discovered that in standard tests developed at the University of Calgary for measuring effectiveness in control of biofilms, 1,3-dibromo-5,5-dimethylhydantoin was effective against Pseudomonas aeruginosa biofilms at levels as small as 1.4 mg/L (total halogen measured as Br2) whereas levels of at least 2.5 mg/L (total halogen measured as Br2) were required when using N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin.
Accordingly, this invention provides, in one of its embodiments, a method of treating water for microbiological control and/or biofilm eradication, said method comprising introducing into the water to be treated an amount of 1,3-dibromo-5,5-dimethylhydantoin that is far less than the amount of N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin required to achieve the same microbiological control and/or biofilm eradication.
Another embodiment of this invention is the method of combating Escherichia coli in an aqueous medium, which method comprises introducing into said medium a biocidally effective amount of 1,3-dibromo-5,5-dimethylhydantoin. This amount is far less than the amount of N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin required to achieve the same level of effectiveness against Escherichia coli. 
Still another embodiment of this invention is the method of combating Enterococcus faecium in an aqueous medium, which method comprises introducing into said medium a biocidally effective amount of 1,3-dibromo-5,5-dimethylhydantoin. This amount is far less than the amount of N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin required to achieve the same level of effectiveness against Enterococcus faecium. 
A preferred embodiment of this invention is the method of concurrently controlling Escherichia coli and Enterococcus faecium in an aqueous medium, which method comprises introducing into the aqueous medium a biocidally effective amount of 1,3-dibromo-5,5-dimethylhydantoin. Here again, the amount of 1,3-dibromo-5,5-dimethylhydantoin required to achieve this concurrent control of Escherichia coli and Enterococcus faecium is much lower than the amount required when, utilizing N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin.
A further embodiment of this invention is the method of eradicating or at least reducing Pseudomonas aeruginosa biofilm on a surface contacted by an aqueous medium, which method comprises introducing into the aqueous medium, a biocidally effective amount of 1,3-dibromo-5,5-dimethylhydantoin to eradicate or substantially eradicate such biofilm. As noted above, this amount of 1,3-dibromo-5,5-dimethylhydantoin is significantly less than the amount of N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin required to achieve the same effectiveness in removal of such biofilm.
Yet another embodiment of this invention is the method of purveying a microbiological control agent for water in accordance with U.S. Environmental Protection Agency regulations, which method comprises purveying a container of a water control agent comprising 1,3-dibromo-5,5-dimethylhydantoin, said container bearing a label having thereon dosage levels pursuant to requirements promulgated by the U.S. Environmental Protection Agency. Typically, this water control agent will be in a compacted form, such as granules, tablets, briquettes, or pucks.
Other embodiments, features, and advantages of this invention will be still further apparent from the ensuing description and appended claims.
Among the features of this invention is the fact that the aforementioned compacted forms can be produced and provided in forms devoid of any binder. This unprecedented feature is now possible by virtue of the fact that 1,3-dibromo-5,5-dimethylhydantoin can be produced, for the first time, having an average particle size of at least about 175 microns. Indeed, 1,3-dibromo-5,5-dimethylhydantoin with average particle sizes of at least about 200 microns, at least about 300 microns, and at least about 600 microns can be produced utilizing process technology described in commonly-owned application Ser. No. 09/484,844, filed Jan. 18, 2000. Preparation of the binder-free compacted forms is described in commonly-owned application Ser. No. 09/484,687, filed Jan. 18, 2000. The disclosures of both of these commonly-owned Applications are incorporated in toto herein by reference.
Yet another feature of this invention is that highly-effective forms of 1,3dibromo-5,5-dimethylhydantoin can also be produced with the aid of novel types of binders which result in the formation of compacted products having superior mechanical and physical properties. Preparation of the compacted forms is described in commonly-owned copending application Ser. No. 09/487,816, filed Jan. 18, 2000, the disclosure of which is incorporated, in toto herein by reference.
Pursuant to further embodiments of this invention, it has been found possible to utilize noncompacted forms of 1,3-dibromo-5,5-dimethylhydantoin in the methods of this invention. Making this possible is the discovery that 1,3-dibromo-5,5-dimethylhydantoin can be produced having large average particle size with superior flowability characteristics enabling the product to be readily discharged from containers in which it is packaged. Moreover, the larger average particle sized product offers the consumer the advantage of having a product which is less prone to caking during storage, especially in warm, humid climates, than the more finely-divided 1,3-dihalo-5,5-dimethylhydantoin products heretofore available in the marketplace. Still another advantage of the large average particle size 1,3-dibromo-5,5-dimethylhydantoin is that, during use, the consumer is not exposed to irritating dusts produced when filling dispensing devices or otherwise dispersing or broadcasting the product into the water to be treated. The only presently known method for producing such large average particle size 1,3-dibromo-5,5-dimethylhydantoin is described in commonly-owned copending application Ser. No. 09/484,844, filed Jan. 18, 2000, the disclosure of which has been incorporated herein.
The methods of this invention thus involve use of 1,3-dibromo-5,5-dimethylhydantoin in compacted or in non-compacted forms. When used in compacted forms, the compacted forms can be produced without use of a binder; provided that the average particle size of the 1,3-dibromo-5,5-dimethylhydantoin is at least 175 microns. Alternatively, the compacted forms can be produced with use of a binder. A preferred type of binder for producing such compacted products is a saturated, normally solid, fatty amide as described in U.S. Pat. No. 5,565,576, issued Oct. 15, 1996 to L. K. Hall, J. A. Falter, and T. E. Farina, the disclosure of which patent is incorporated herein in toto as if fully set forth herein. In the practice of this invention such fatty amide binder is used with 1,3-dibromo-5,5-dimethylhydantoin having an average particle size of at least 175 microns. A particularly preferred type of binder for use in producing the compacted forms of 1,3-dibromo-5,5-dimethylhydantoin for use in this invention is a micronized synthetic polyolefin-based hydrocarbon wax and/or a micronized synthetic polyfluorocarbon wax effective to form the compacted product, provided the wax is suitably compatible with the 1,3-dibromo-5,5-dimethylhydantoin. In the practice of this invention with compacted forms of blends of 1,3-dibromo-5,5-dimethylhydantoin with a micronized synthetic polyolefin-based hydrocarbon wax and/or a micronized synthetic polyfluorocarbon wax, the average particle size of the 1,3-dibromo-5,5xe2x80x2-dimethylhydantoin can be in the range of about 20 to about 600 microns, but preferably the average particle size of the 1,3-dibromo-5,5-dimethylhydantoin is in the range of about 175 to about 400 microns, if not even greater.
The amount of 1,3-dibromo-5,5-dimethylhydantoin used in practicing the methods of this invention is a biocidally effective amount, e.g., an amount which is at least sufficient to achieve substantial microbiological control, if not complete microbiological control, in the water being treated and/or substantial biofilm eradication,: if not complete biofilm eradication, from the surfaces in contact with the water system being treated. Typically, dosages of 1,3-dibromo-5,5-dimethylhydantoin used for this purpose will fall within the range of about 0.2 to about 10 milligrams of bromine, as Br2, per liter of water. Preferably, such dosages are in the range of about 0.2 to about. 5 milligrams of bromine, as Br2, per liter of water. However, departures from these ranges are permissible provided that the departures result in sufficient microbiological control in accordance with the needs of the occasion, including applicable governmental regulations.
In order to demonstrate the efficacy of this invention, a series of tests was conducted on our behalf by an independent microbiology and virology; laboratory. One such series of tests, which utilized the AOAC Official Method referred to hereinabove, involved determinations of microbiological control against E. coli bacteria. Another set of tests involved determinations of microbiological control against E. faecium. In each case, comparative tests were carried out in the same manner utilizing N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin. Briefly, the test involves exposing a culture of the microorganism to various concentrations of bromine solution prepared from an aqueous stock solution of the compound under test. At various time intervals the bromine in the test suspensions is chemically neutralized, and the amount of viable bacteria remaining is enumerated by plating onto nutrient agar and incubating for 2 days at 37xc2x0 C. Results are expressed at the log10 colony forming units (CFU). The concentration of the compound required to achieve complete kill (i.e., no viable bacteria remain) within 30 seconds is determined in the test and reported to the U.S. Environmental Protection Agency to support the product registration as a disinfectant for swimming pools. Such testing is one of the requirements needed for product registration with the EPA, which in turn enables the product to be purveyed with labeling showing the efficacious dosage level of the product.
Table 1 summarizes the data obtained in the tests using respectively, 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) and N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin (BCDMH) and in which the microorganism in each case was E. coli. It can be seen that 1,3-dibromo-5,5-dimethylhydantoin passes the test at one milligram of1bromine, as Br2, per liter of water, as evidenced by the complete kill within 30 seconds, whereas N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin requires two milligrams of bromine, as Br2, per liter to of water to achieve complete kill within 30 seconds.
Table 2 summarizes the data obtained in the tests using respectively 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) and N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin (BCDMH) and in which the microorganism in each case was E. faecium. Table 2 shows that 1,3-dibromo-5,5-dimethylhydantoin passes the test at one milligram of bromine, as Br2, per liter of water, as evidenced by the complete kill within 30 seconds, whereas N,Nxe2x80x2-bromochloro-5,5-dimethylhydantoin requires two milligrams of bromine, as Br2, per liter of water to achieve complete kill within 30 seconds.
Table 3 summarizes test results performed at MBEC Biofilm Technologies, Inc., Calgary, Canada on the effectiveness of various biocides on biofilm removal. The test procedure, developed at the University of Calgary, utilizes a device which allows the growth of 96 identical biofilms under carefully controlled conditions. The device consists of a two-part vessel comprised of an upper plate containing 96 pegs that seals against a bottom plate. The bottom plate can consist of either a trough (for biofilm growth) or a standard 96-well plate (for biocide challenge). The biofilms develop on the 96 pegs. The device has been used as a general method for evaluating the efficacy of antibiotics and biocides towards biofilms. See in this connection H. Ceri, et al., xe2x80x9cThe MBEC Test: A New In Vitro Assay Allowing Rapid Screening for Antibiotic Sensitivity of Biofilmxe2x80x9d, Proceedings of the ASM, 1998, 89, 525; Ceri, et al., xe2x80x9cAntifungal and Biocide Susceptibility testing of Candida Biofilms using the MBEC Devicexe2x80x9d, Proceedings of the Interscience Conference on Antimicrobial Agents and Chemotherapy, 1998, 38, 495; and H. Ceri, et al., xe2x80x9cThe Calgary Biofilm Device: A New Technology for the Rapid Determination of Antibiotic Susceptibility of Bacterial Biofilmsxe2x80x9d, Journal of Clinical Microbiology, 1999, 37, 1771-1776.
Six biocide systems were evaluated using the above test procedure and test equipment. Five of these systems were oxidizing biocides, viz., chlorine.(from NaOCl), halogen (from NaOCl+NaBr), halogen (from BCDMH), bromine (from DBDMH), and chlorine (from trichloroisocyanuric acid), all expressed as bromine as Br2 in mg/L, so that all test results were placed on the same basis. The sixth biocide was glutaraldehyde, a non-oxidizing biocide.
These biocide systems were used to challenge biofilms of Pseudomonas aeruginosa (ATCC 15442). This is a Gram (xe2x88x92) bacterium which is ubiquitous in microbiological slimes found in industrial and recreational water systems. See in this connection J. W. Costerton and H. Anwar, xe2x80x9cPseudomonas aeruginosa: The Microbe and Pathogenxe2x80x9d, in Pseudomonas aeruginosa Infections and Treatment, A. L. Baltch and R. P. Smith editors, Marcel Dekker publishers, New York, 1994.
In Table 3 the MBEC (minimum biofilm eradication concentration) results presented are for the one-hour biocide contact time used in the test. The values given for the halogen containing biocides are expressed in terms of mg/L of bromine as Br2. The data on the glutaraldehyde is in terms of mg/L as active ingredient. The data indicate that the DBDMH used pursuant to this invention was more effective than any of the other biocides tested under these conditions with an MBEC of 1.4 mg/L of bromine, as Br2. In fact, only slightly more than one-half as much bromine from DBDMH was required to remove the biofilm as compared to the total halogen, expressed as Br2, that was required from BCDMH.